LXR busybox/coreutils/tail.c

   1/* vi: set sw=4 ts=4: */
   2/*
   3 * Mini tail implementation for busybox
   4 *
   5 * Copyright (C) 2001 by Matt Kraai <kraai@alumni.carnegiemellon.edu>
   6 *
   7 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
   8 */
   9
  10/* BB_AUDIT SUSv3 compliant (need fancy for -c) */
  11/* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
  12/* http://www.opengroup.org/onlinepubs/007904975/utilities/tail.html */
  13
  14/* Mar 16, 2003      Manuel Novoa III   (mjn3@codepoet.org)
  15 *
  16 * Pretty much rewritten to fix numerous bugs and reduce realloc() calls.
  17 * Bugs fixed (although I may have forgotten one or two... it was pretty bad)
  18 * 1) mixing printf/write without fflush()ing stdout
  19 * 2) no check that any open files are present
  20 * 3) optstring had -q taking an arg
  21 * 4) no error checking on write in some cases, and a warning even then
  22 * 5) q and s interaction bug
  23 * 6) no check for lseek error
  24 * 7) lseek attempted when count==0 even if arg was +0 (from top)
  25 */
  26
  27//kbuild:lib-$(CONFIG_TAIL) += tail.o
  28
  29//usage:#define tail_trivial_usage
  30//usage:       "[OPTIONS] [FILE]..."
  31//usage:#define tail_full_usage "\n\n"
  32//usage:       "Print last 10 lines of each FILE (or stdin) to stdout.\n"
  33//usage:       "With more than one FILE, precede each with a filename header.\n"
  34//usage:     "\n        -f              Print data as file grows"
  35//usage:     "\n        -c [+]N[kbm]    Print last N bytes"
  36//usage:     "\n        -n N[kbm]       Print last N lines"
  37//usage:     "\n        -n +N[kbm]      Start on Nth line and print the rest"
  38//usage:        IF_FEATURE_FANCY_TAIL(
  39//usage:     "\n        -q              Never print headers"
  40//usage:     "\n        -s SECONDS      Wait SECONDS between reads with -f"
  41//usage:     "\n        -v              Always print headers"
  42//usage:     "\n        -F              Same as -f, but keep retrying"
  43//usage:     "\n"
  44//usage:     "\nN may be suffixed by k (x1024), b (x512), or m (x1024^2)."
  45//usage:        )
  46//usage:
  47//usage:#define tail_example_usage
  48//usage:       "$ tail -n 1 /etc/resolv.conf\n"
  49//usage:       "nameserver 10.0.0.1\n"
  50
  51#include "libbb.h"
  52
  53struct globals {
  54        bool from_top;
  55        bool exitcode;
  56} FIX_ALIASING;
  57#define G (*(struct globals*)&bb_common_bufsiz1)
  58#define INIT_G() do { } while (0)
  59
  60static void tail_xprint_header(const char *fmt, const char *filename)
  61{
  62        if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
  63                bb_perror_nomsg_and_die();
  64}
  65
  66static ssize_t tail_read(int fd, char *buf, size_t count)
  67{
  68        ssize_t r;
  69
  70        r = full_read(fd, buf, count);
  71        if (r < 0) {
  72                bb_perror_msg(bb_msg_read_error);
  73                G.exitcode = EXIT_FAILURE;
  74        }
  75
  76        return r;
  77}
  78
  79#define header_fmt_str "\n==> %s <==\n"
  80
  81static unsigned eat_num(const char *p)
  82{
  83        if (*p == '-')
  84                p++;
  85        else if (*p == '+') {
  86                p++;
  87                G.from_top = 1;
  88        }
  89        return xatou_sfx(p, bkm_suffixes);
  90}
  91
  92int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  93int tail_main(int argc, char **argv)
  94{
  95        unsigned count = 10;
  96        unsigned sleep_period = 1;
  97        const char *str_c, *str_n;
  98
  99        char *tailbuf;
 100        size_t tailbufsize;
 101        unsigned header_threshhold = 1;
 102        unsigned nfiles;
 103        int i, opt;
 104
 105        int *fds;
 106        const char *fmt;
 107        int prev_fd;
 108
 109        INIT_G();
 110
 111#if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
 112        /* Allow legacy syntax of an initial numeric option without -n. */
 113        if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
 114         && isdigit(argv[1][1])
 115        ) {
 116                count = eat_num(argv[1]);
 117                argv++;
 118                argc--;
 119        }
 120#endif
 121
 122        /* -s NUM, -F imlies -f */
 123        IF_FEATURE_FANCY_TAIL(opt_complementary = "s+:Ff";)
 124        opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:vF"),
 125                        &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
 126#define FOLLOW (opt & 0x1)
 127#define COUNT_BYTES (opt & 0x2)
 128        //if (opt & 0x1) // -f
 129        if (opt & 0x2) count = eat_num(str_c); // -c
 130        if (opt & 0x4) count = eat_num(str_n); // -n
 131#if ENABLE_FEATURE_FANCY_TAIL
 132        /* q: make it impossible for nfiles to be > header_threshhold */
 133        if (opt & 0x8) header_threshhold = UINT_MAX; // -q
 134        //if (opt & 0x10) // -s
 135        if (opt & 0x20) header_threshhold = 0; // -v
 136# define FOLLOW_RETRY (opt & 0x40)
 137#else
 138# define FOLLOW_RETRY 0
 139#endif
 140        argc -= optind;
 141        argv += optind;
 142
 143        /* open all the files */
 144        fds = xmalloc(sizeof(fds[0]) * (argc + 1));
 145        if (!argv[0]) {
 146                struct stat statbuf;
 147
 148                if (fstat(STDIN_FILENO, &statbuf) == 0
 149                 && S_ISFIFO(statbuf.st_mode)
 150                ) {
 151                        opt &= ~1; /* clear FOLLOW */
 152                }
 153                argv[0] = (char *) bb_msg_standard_input;
 154        }
 155        nfiles = i = 0;
 156        do {
 157                int fd = open_or_warn_stdin(argv[i]);
 158                if (fd < 0 && !FOLLOW_RETRY) {
 159                        G.exitcode = EXIT_FAILURE;
 160                        continue;
 161                }
 162                fds[nfiles] = fd;
 163                argv[nfiles++] = argv[i];
 164        } while (++i < argc);
 165
 166        if (!nfiles)
 167                bb_error_msg_and_die("no files");
 168
 169        /* prepare the buffer */
 170        tailbufsize = BUFSIZ;
 171        if (!G.from_top && COUNT_BYTES) {
 172                if (tailbufsize < count + BUFSIZ) {
 173                        tailbufsize = count + BUFSIZ;
 174                }
 175        }
 176        /* tail -c1024m REGULAR_FILE doesn't really need 1G mem block.
 177         * (In fact, it doesn't need ANY memory). So delay allocation.
 178         */
 179        tailbuf = NULL;
 180
 181        /* tail the files */
 182
 183        fmt = header_fmt_str + 1; /* skip leading newline in the header on the first output */
 184        i = 0;
 185        do {
 186                char *buf;
 187                int taillen;
 188                int newlines_seen;
 189                unsigned seen;
 190                int nread;
 191                int fd = fds[i];
 192
 193                if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 194                        continue; /* may happen with -F */
 195
 196                if (nfiles > header_threshhold) {
 197                        tail_xprint_header(fmt, argv[i]);
 198                        fmt = header_fmt_str;
 199                }
 200
 201                if (!G.from_top) {
 202                        off_t current = lseek(fd, 0, SEEK_END);
 203                        if (current > 0) {
 204                                unsigned off;
 205                                if (COUNT_BYTES) {
 206                                /* Optimizing count-bytes case if the file is seekable.
 207                                 * Beware of backing up too far.
 208                                 * Also we exclude files with size 0 (because of /proc/xxx) */
 209                                        if (count == 0)
 210                                                continue; /* showing zero bytes is easy :) */
 211                                        current -= count;
 212                                        if (current < 0)
 213                                                current = 0;
 214                                        xlseek(fd, current, SEEK_SET);
 215                                        bb_copyfd_size(fd, STDOUT_FILENO, count);
 216                                        continue;
 217                                }
 218#if 1 /* This is technically incorrect for *LONG* strings, but very useful */
 219                                /* Optimizing count-lines case if the file is seekable.
 220                                 * We assume the lines are <64k.
 221                                 * (Users complain that tail takes too long
 222                                 * on multi-gigabyte files) */
 223                                off = (count | 0xf); /* for small counts, be more paranoid */
 224                                if (off > (INT_MAX / (64*1024)))
 225                                        off = (INT_MAX / (64*1024));
 226                                current -= off * (64*1024);
 227                                if (current < 0)
 228                                        current = 0;
 229                                xlseek(fd, current, SEEK_SET);
 230#endif
 231                        }
 232                }
 233
 234                if (!tailbuf)
 235                        tailbuf = xmalloc(tailbufsize);
 236
 237                buf = tailbuf;
 238                taillen = 0;
 239                /* "We saw 1st line/byte".
 240                 * Used only by +N code ("start from Nth", 1-based): */
 241                seen = 1;
 242                newlines_seen = 0;
 243                while ((nread = tail_read(fd, buf, tailbufsize - taillen)) > 0) {
 244                        if (G.from_top) {
 245                                int nwrite = nread;
 246                                if (seen < count) {
 247                                        /* We need to skip a few more bytes/lines */
 248                                        if (COUNT_BYTES) {
 249                                                nwrite -= (count - seen);
 250                                                seen += nread;
 251                                        } else {
 252                                                char *s = buf;
 253                                                do {
 254                                                        --nwrite;
 255                                                        if (*s++ == '\n' && ++seen == count) {
 256                                                                break;
 257                                                        }
 258                                                } while (nwrite);
 259                                        }
 260                                }
 261                                if (nwrite > 0)
 262                                        xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
 263                        } else if (count) {
 264                                if (COUNT_BYTES) {
 265                                        taillen += nread;
 266                                        if (taillen > (int)count) {
 267                                                memmove(tailbuf, tailbuf + taillen - count, count);
 268                                                taillen = count;
 269                                        }
 270                                } else {
 271                                        int k = nread;
 272                                        int newlines_in_buf = 0;
 273
 274                                        do { /* count '\n' in last read */
 275                                                k--;
 276                                                if (buf[k] == '\n') {
 277                                                        newlines_in_buf++;
 278                                                }
 279                                        } while (k);
 280
 281                                        if (newlines_seen + newlines_in_buf < (int)count) {
 282                                                newlines_seen += newlines_in_buf;
 283                                                taillen += nread;
 284                                        } else {
 285                                                int extra = (buf[nread-1] != '\n');
 286                                                char *s;
 287
 288                                                k = newlines_seen + newlines_in_buf + extra - count;
 289                                                s = tailbuf;
 290                                                while (k) {
 291                                                        if (*s == '\n') {
 292                                                                k--;
 293                                                        }
 294                                                        s++;
 295                                                }
 296                                                taillen += nread - (s - tailbuf);
 297                                                memmove(tailbuf, s, taillen);
 298                                                newlines_seen = count - extra;
 299                                        }
 300                                        if (tailbufsize < (size_t)taillen + BUFSIZ) {
 301                                                tailbufsize = taillen + BUFSIZ;
 302                                                tailbuf = xrealloc(tailbuf, tailbufsize);
 303                                        }
 304                                }
 305                                buf = tailbuf + taillen;
 306                        }
 307                } /* while (tail_read() > 0) */
 308                if (!G.from_top) {
 309                        xwrite(STDOUT_FILENO, tailbuf, taillen);
 310                }
 311        } while (++i < nfiles);
 312        prev_fd = fds[i-1];
 313
 314        tailbuf = xrealloc(tailbuf, BUFSIZ);
 315
 316        fmt = NULL;
 317
 318        if (FOLLOW) while (1) {
 319                sleep(sleep_period);
 320
 321                i = 0;
 322                do {
 323                        int nread;
 324                        const char *filename = argv[i];
 325                        int fd = fds[i];
 326
 327                        if (FOLLOW_RETRY) {
 328                                struct stat sbuf, fsbuf;
 329
 330                                if (fd < 0
 331                                 || fstat(fd, &fsbuf) < 0
 332                                 || stat(filename, &sbuf) < 0
 333                                 || fsbuf.st_dev != sbuf.st_dev
 334                                 || fsbuf.st_ino != sbuf.st_ino
 335                                ) {
 336                                        int new_fd;
 337
 338                                        if (fd >= 0)
 339                                                close(fd);
 340                                        new_fd = open(filename, O_RDONLY);
 341                                        if (new_fd >= 0) {
 342                                                bb_error_msg("%s has %s; following end of new file",
 343                                                        filename, (fd < 0) ? "appeared" : "been replaced"
 344                                                );
 345                                        } else if (fd >= 0) {
 346                                                bb_perror_msg("%s has become inaccessible", filename);
 347                                        }
 348                                        fds[i] = fd = new_fd;
 349                                }
 350                        }
 351                        if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 352                                continue;
 353                        if (nfiles > header_threshhold) {
 354                                fmt = header_fmt_str;
 355                        }
 356                        for (;;) {
 357                                /* tail -f keeps following files even if they are truncated */
 358                                struct stat sbuf;
 359                                /* /proc files report zero st_size, don't lseek them */
 360                                if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
 361                                        off_t current = lseek(fd, 0, SEEK_CUR);
 362                                        if (sbuf.st_size < current)
 363                                                xlseek(fd, 0, SEEK_SET);
 364                                }
 365
 366                                nread = tail_read(fd, tailbuf, BUFSIZ);
 367                                if (nread <= 0)
 368                                        break;
 369                                if (fmt && (fd != prev_fd)) {
 370                                        tail_xprint_header(fmt, filename);
 371                                        fmt = NULL;
 372                                        prev_fd = fd;
 373                                }
 374                                xwrite(STDOUT_FILENO, tailbuf, nread);
 375                        }
 376                } while (++i < nfiles);
 377        } /* while (1) */
 378
 379        if (ENABLE_FEATURE_CLEAN_UP) {
 380                free(fds);
 381                free(tailbuf);
 382        }
 383        return G.exitcode;
 384}
 385